The microbial contaminants and chemical pollutants in air can be cleaned by the way of adsorption, photocatalysis, anion, plasma, and ozone etc. Of these methods, purification by utilizing high concentration of ozone is considered to be the most effective. The standard electrode potential of ozone is 2.07 volt, and the chemical reaction rate constant is 101˜102 L/(mol·s). In its gas phase, ozone can eliminate mold (one of the microbiological contamination that is relatively difficult to eliminate) within 100 minutes, but ozone purification has its shortcomings. Ozone is harmful to humans, hence man-machine coexistence cannot be realized during the disinfection and the purification process. Meanwhile, .OH has stronger oxidizing ability (with a standard electrode potential of 2.80 volt), almost has the same oxidizing ability as the elemental fluorine (with a standard electrode potential of 2.87 volts), and thus is a very strong oxidizing substance. Meanwhile, the .OH reaction is a kind of free-radical reaction, and has a very high chemical reaction rate of 107˜109 L/(mol·s), and can react seven order of magnitude faster than ozone. The chemical reaction time is less than 1 second, and the biochemical reaction time is between 1 to 10 seconds. However, as .OH is very short-lived (only around 10 nano seconds), the generation of .OH and the pollution purification should proceed at the same time. It means that the in situ regeneration of high concentration of free radicals in gas phase or mass generation of free radicals in gas phase such as .OH, .ClO2, .HO2 and .O need to be achieved.
The surface of silica is highly hydrophilic, and water molecule can be reversibly or irreversibly adsorbed on the surface. Hence the surface of silica is normally covered with a layer of OH (Hydroxyl group) and water molecules. The former mentioned hydroxyl group binds to the Si atoms on the surface which is chemically adsorbed. The latter mentioned water molecule is adsorbed on the surface physically. Based on a large amount of experimental data, through long time observation as well as theoretical analysis, this characteristic of silica helps us in achieving the goal of mass generation of free radicals in gas phase, such as .OH, .ClO2, .HO2 and .O. When silica is loaded with stabilized chlorine dioxide solution, then dehydrated at a temperature under 85° C., in the absence of light or heat, ClO2 can cause the physically adsorbed water layer (in small amount) on the silica surface to go through ionized hydrolysis, H2O—H++OH−, and the following hydrolysis can take place ClO2+H2O—HClO2+HClO3. Other than this hydrolysis, there also exists nonionic chemical hydrolysis as following,

The above nonionic chemical hydrolysis (in the pattern of free radicals) is not significant in general, however, at the presence of physical or chemical catalyst or the presence of substrate that can react with it, the reaction rate can be accelerated greatly, and large amount of .OH can be generated,

As the surface of active aluminium oxide is also covered with a layer of OH generated by the water adsorbed, it has the same characteristic as the aforementioned silica.
Advanced oxidation technology is marked by the production of .OH. However, current methods of generating gas phase .OH, such as patent No. CN201010567135.8 and patent No. CN201310700249.9, require additional equipment and the cost is very high, thus make them difficult to be used in large scale industrial production.